1. Field of the Invention
This invention relates to a motion detection system for boats, and particularly to the use of a motion detector mounted on an anchor for detecting dragging of the anchor. A sonar wave is generated when the anchor drags, and an alarm on the boat is actuated when the sonar signal is received. In one embodiment, an RF signal is produced to actuate the alarm.
2. Description of the Prior Art
When it is desired to maintain a boat in a specific position in the water, an anchor attached to an anchor line is dropped into the water to engage the bottom. The anchor flukes engage or dig into the bottom to secure the boat, and absent unusual conditions the boat will be held in the desired position with little or no drift. However high winds, turbulent seas or shifts in tide or current often cause the anchor to free itself from the bottom, and to drag along the bottom at the end on the anchor line. When this occurs, the boat is no longer secure, and is subject to random drifting, a situation which is potentially dangerous. It is desirable to warn the crew or a responsible person when the anchor is no longer secure on the bottom so that corrective action may be taken.
A number of prior art devices or systems attempt to solve the problem of a dragging anchor by sounding an alarm when an anchor becomes disengaged from the bottom. Many of these devices or systems require the use of a secondary or auxiliary anchor or weight attached to a separate line and dropped to the bottom from the boat, movement of the boat in relation to the auxiliary anchor being sensed and an alarm actuated in response thereto. One example of this type of warning system is shown in U.S. Pat. No. 3,727,212 to Jones, in which a weight is secured via a line to a vertically extending control arm, and the weight is dropped to the bottom. Any movement of the control arm actuates an alarm. Control systems of this type are often oversensitive to tide shifts, insensitive to slow drift, and heavy and bulky.
Another type of anchor-dragging alarm is described in U.S. Pat. No. 3,579,182 to Schneider, in which an anchor-mounted electrical switch is actuated when the anchor shank inclines itself vertically rather than the usual horizontal position it assumes when embedded in the bottom. Conducting wires extend from the anchor-mounted switch through tubing tied together with the anchor line. An electrical signal is passed from the switch through the conducting wires to an alarm on the boat when the anchor deviates substantially from the horizontal. A disadvantage of this type of system is the need for relatively fragile electrical wires extending from the anchor to the boat, and the possibility of damage to the conductors. This signal upon movement or dragging of the anchor.
Another anchor drag indicator is shown in U.S. Pat. No. 3,831,139 to Hennessey, wherein a motion responsive floating shell containing an electrical switch produces an electrical output signal when disturbed from its normal orientation. This device requires electrical power to be supplied to it, and also requires that the output electrical signal be fed through wires to the boat.
It is an object of this invention to provide an anchor alarm system for boats which senses dragging of the anchor and which eliminates the need for electrical connection between the anchor and the boat.
A further object of this invention is a motion sensor for boat anchors which produces an acoustic signal in the water upon motion of the anchor.
A still further object of this invention is a boat alarm system in which receipt of an acoustic signal indicative of movement of the anchor initiates an RF radio signal which may be received and used to trigger an alarm on the boat and/or at a remote location.